Massachusetts officials wanted a large span over the Mystic River decades before they got one. The Great Depression made such an expense prohibitive (the bridge was eventually built for $27 million), and commuters relied on the Chelsea North Bridge, a small two-lane affair plagued by the inconvenient need to swing open for shipping. The Mystic River Bridge opened for traffic on Feb. 26, 1950, and was renamed in honor of former Boston mayor and Massachusetts governor Maurice J. Tobin in 1967. When a truck slammed into a bridge support in 1973, part of the upper deck collapsed and two months passed before it could again carry traffic. Today the Tobin Bridge hosts 85,000 vehicles daily over its almost 12,000-foot length.

In this May 4, 1949, photo, with the lower half of the Mystic River Bridge completed, forms went up for concreting the upper pedestals. To reach the top of the forms, the builders pumped concrete 132 feet straight up. This photograph shows Pier M-3 completed on the Chelsea side. The closeness of the old swing bridge created construction problems while the deepwater piers were being built.